type of __fspath__().

As part of this change, also make sure that the pure Python
implementation of os.fspath() is tested.

dictproxy was used in Python 2 and it was renamed to mappingproxy
in Python 3.3.

Patch by Julien.

Patch by Matt Morrison.

Several test cases in distutils use PyPIRCCommandTestCase as
their base class and as a result of that the following tests
were ran more than once:

* test_server_registration
* test_server_empty_registration
* test_config_interpolation

This commit moves the infrastructure used by other tests
into a new BasePyPIRCCommandTestCase class.

Patch by Yoni Lavi

Rest of patch that should not be cherry picked into 3.5.2 final.

Fix code and tests that fail with this restriction.
Fix htests to not create a second and redundant root and mainloop.

load() and loads() functions and JSONEncoder and JSONDecoder class
constructors in the json module are now keyword-only.

I noticed that there is no test for this feature while doing
triaging work on pypa/pypi-legacy.